Transmission SAXS (tSAXS) has been identified as a potential solution for measuring nanoscale features by interrogating structures with sub-nanometer wavelength X-ray radiation. Most relevant parameters describing critical dimensions (CDs) of nanoscale features are pitch, pitch variations, side wall angle, line edge roughness, line width roughness and so forth. Based on the spacing of diffraction peaks, the parameter (pitch) can be extracted from the tSAXS scattering pattern. The geometric form factors of a structure can be extracted from the envelope function of the scattering intensity. In addition to the CDs of a structure, tSAXS has been used to successfully characterize LER, pitch walk, non-planar film thicknesses on sidewalls and complicated profiles of a memory structure that requires a 6-trapezoid model. Since the X-ray wavelength is still much smaller than the feature size of today's nanoscale structure, the tSAXS technique will stay as a viable CD metrology in the future. Actually the applicability of tSAXS will improve at future technology nodes where more densely packed features or an ever decreasing pitch will result in widely apart scattering peaks; thus, more readily detectable via tSAXS. Additionally, it avoids the issues related to optical properties, e.g. n and k, their wavelength and size dependences since tSAXS is based on classical X-ray elastic scattering, the observed scattering intensity depends only on variation in local electron density.